Electromechanical control system



Jan. 20,` 1942. w v, WQLFE 2,270,367

ELEGTROMEGHANICAL CONTROL SYSTEM Filed Mayl 51, 19:59

Patented Jan. 20, 1942 Wallace v. Wolfe,

Radio Corporationv of America, a corporation of Delaware Application May 31, 1939, Serial No. 276,549

4 claims. (ol. 179-1003) Thisinvention relates to electrical control circuits and particularly rangement for neutralizing undesired resonance characteristics in an electrical element.

' In the art of sound recording, a well known method of and system for modulating a light beam being impressed upon a sound track area of a film is by the use of 4a galvanometer having a moving armature which tilts a mirror for deflecting the beam transversely of the film. The armature of the galvanometer isy actuated .by a magnetic field produced by a coil connected to the output of the speech or audio-frequency amplifying equipment which, in turn, may be connected to a microphone or other translating device, such as a phonograph pickup or the like. The armature ofthe galvanometer is usually tensioned, which produces a mechanical resonance at one or more frequencies, while there may freq'ilently be an electrical resonant point somewhere in the system.

In view of these conditions, the deflection of the mirror is not uniform for the same current input from the speech amplifying equipment at varying frequencies, thus causing distortion of the sound being impressed upon the film. For optimum operation, the frequencyresponse characteristic of the galvanometer should be flat over the entire frequency range.

The present invention minimizes the effect of any distortion of the galvanometer frequency characteristic and thereby permits of greater tolerances in the manufacture of the galvanometer and the electrical circuit used therewithr In brief, the operation of the invention is that voltages in accordance with the frequency-response `characteristic of the galvanometer are generated and these voltages, which are directly and solely proportional to the armature movements, are amplied, reversed in phase and fed back into the speech input amplifying system. Since the feedback voltages are in phase opposition to the original voltages, a cancellation or neutralization will take place in the electrical circuit, thereby producing the flat frequency characteristic desired.

The generation of the feedback voltages is accomplished by placing a second coil, in addition to the galvanometer armature actuating coil, in a non-inductive coupling relationship thereto so that the second coil has induced therein voltages due solely to movements of the armature. v

to a feedback circuit arl The principal object of the invention, therefore, is to improve the operation of an electromechanical device.

Another object of the invention is to maintain a constant relationship between frequency input and the response of a moving element actuated by electrical currents.

A further? object of the invention is to reintroduce into an amplifying system voltages divrectly proportional to and generated by movements Vcaused by electrical currents originating from this amplifying system.

A further object of the invention is to provide a feedback circuitv for a sound recording galvanometer wherein the feedback voltages are generated within the galvanometer itself.`

Although the novel featuresy which areAv believedv to' be characteri'sticl of this invention are 'pointed outwith-- particularity inthe claims appended herewith, the manner of its organization and the mode of its operation will be better understood by referring to the following description read in conjunction with the accompanying drawing forming a part thereof in which Fig. 1 is a diagrammatic arrangement of a sound recording system embodying the invention; and

Fig. 2 is a graph showing characteristics of the system and the manner of its operation.

Referring now to Fig. 1, a microphone 5 feeds an audio frequency or speech input amplifier 6. The output of the amplifler 6 is fed into an actuating coil 8 of a galvanometer having a movable armature 9 which tilts or vibrates a mirror l0 in accordance with the amplitude and frequency of the sound waves to be recorded. The light source of the apparatus comprises a lamp represented by a filament l2, the light therefrom being projected through a lens and mask unit I3 to the mirror I0 of the galvanometer. Reflected light from the mirror is projected to a film I5 through an optical slit assembly I6. A well known type of sound recording system so represented is disclosed and claimed in U. S. Patents 2,102,776, 2,102,777 and 2,102,778.

`To obtain the voltages produced by the actual movement of the armature 9, a second pickup coil 20 is mounted on the so that no inductive coupling exists between the actuating coil 8 and the pickup coil 20. The Voltage induced in the coil 20 is fed into an amplier 2l and then to two series connected, phase and amplitude correcting bridge units 22 and 23, these units being of the type illustrated in U. S. Patent 2,011,566 lof August 20, 1935. The

armature in a manner frequency region, lower region and particularly high in the upper frequency region. This last peak is caused by mechanical resonance. However, with the particunance peak occurring cycles, but also the smaller variations in response. On the graph shown in Fig. 2 is a dotted curve .coil 20 is directly proportional to the movements of the armature, a voltage proportional to curve A will be impressed upon the amplier 2| from coil 20. Since this voltage is reversed in phase and fed back to the galvanometer frequency response.

I claim as my invention:

1. In a sound recording system, the combination of means for producing a light beam, means for projecting said beam to la film, a mirror for vibrating said beam with respect to said lm, a

inductance having generated therein voltages directly proportional to the movements of said armature and said mirror.

2. A sound recording system in accordance with claim 1 in which means are provided for feeding back said generated voltages to said current impressing means in a different phase relationship than they originally existed in said means.

3. In a sound recording system, the combination of means for producing a light beam, means therein voltages directly proportional to the said vibrations of said armature caused by said rstmentioned coil.

4. A sound recording system in accordance with is connected between the output of said second amplifier and the input to said rst-mentioned amplier.

WALLACE V. WOLFE. 

